1. Field of the Invention
The present invention relates to a vacuum pump including two one- or two-stage gas friction pumps and a multistage pump arranged downstream of the two gas friction pumps.
2. Description of the Prior Art
For producing a high vacuum, combination of different types of vacuum pumps are necessary. This is because the pressure region, which is further away from the atmospheric pressure and closer to a pressure of about 104 mbar and lower, has several flow regions in which physical characteristics of the conditions and streams of gasses are subjected to different physical laws.
Thus, for producing a high vacuum, at least two different vacuum pumps having different operational characteristics are combined. For example, a pump stand can include a turbomolecular pump, and a vane rotary pump dischargeable into atmosphere. Pump stands, which consist of at least two vacuum pumps necessary to achieve the required vacuum-technical parameters such as pressure ratios and suction speeds, have serious drawback. These drawbacks consist in that they are expensive and require a relatively large mounting space. Each pump requires its own drive with a power supply, independent monitoring and control, and its own bearing system. The connections between the two pumps, with appropriate valves, and separate control units increase the costs of such pump stands.
Accordingly, an object of the present invention is to provide a single vacuum pump capable of operating in the entire pressure range from the atmospheric pressure to pressure of 14 mbar and lower.
Another object of the present invention is to provide a vacuum pump formed as single compact apparatus so that the drawbacks of multi-pump stands are eliminated.
A further object of the present invention is to provide a vacuum pump having adequately high pressure ratio and suction speed capable of meeting the requirements of the fields of their application.
A still further object of the present invention is to provide a vacuum pump reliable in operation.
A yet another object of the present invention is to provide a vacuum pump with a lubrication-free operation at the high-vacuum side.
These and other objects of the present invention, which will become apparent herein after are achieved by providing a vacuum pump including suction and discharge regions and two gas friction pumps arranged on opposite sides of the suction region and parallel to each other in a gas flow direction from the suction region to the discharge region. Each of the gas friction pumps has at least one stage and a discharge region. The pump further includes channels connecting the discharge regions of the two gas friction pumps and providing for gas flow from the discharge regions of the two gas friction pumps into a common discharge region of the two gas friction pumps. A multi-stage pump is located downstream of both gas friction pumps for compressing the gas flowing through the multi-stage pump.
The multi-stage pump has a suction region and a discharge region connected with the discharge region of the vacuum pump, and a conduit for connecting the common discharge region of the two gas friction pumps with the suction region of the downstream multi-stage pump.
The present invention provides a compact vacuum pump covering the entire pressure region from the atmospheric pressure to the high vacuum pressure. The parallel arrangement of gas friction pumps at the high-vacuum side provides for a double-flow suction region whereby a high suction speed becomes possible. The aspirated gas is adequately compressed within the gas friction pumps so that the subsequent pump can be formed as a single-flow pump.
This combination, together with the feature that the two gas streams are combined within the gas friction pump unit and enter the following suction chamber of the multi-stage pump as a single stream, insures a compact constructions with reduced dimensions which noticeably reduce the manufacturing and mounting costs. A stable support is provided by arranging the shaft bearings on both sides of the rotor, which also permits to use bearing having a smaller diameter. Such bearings provide for operation without problem and high rotational speeds. In addition, the bearings are separated from the high vacuum side by the gas friction pumps, whereby a lubrication-free environment is created at the high-vacuum side.
For constructive and operational reasons, it is advantageous to form the gas friction pumps as Holweck pumps. Those are particularly suitable as they can be fitted in a narrow space and permit to achieve a maximal pressure ratio. The double-flow arrangement permits to achieve a required suction speed.
As a subsequent pump, advantageously, a peripheral pump can be used. Such a pump is particular suitable for compression of the gas discharged by the two gas friction pumps.
A big advantage is achieved when the stator elements of the peripheral pump are formed as discs abutting each other. In conventional designs, in which the stator discs are separated by rotor discs, a returned flow through the clearances between the discs can take place, which increase losses and substantially reduces the pressure ratio. The above-discussed drawback of the conventional peripheral pumps is eliminated by arranging, according to the present invention, the stator elements, the stator discs, in abutting relationship with each other, which is only then possible when, according to the present invention, the rotor elements are secured on the rotor shaft with camp rings. Only under these conditions, the rotor elements can be arranged one after another with an optimal axial backlash.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood form the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.